Planning Storage Configurations

There are many factors to consider when selecting hardware for use by Microsoft Exchange Server 2007. Three of the most critical factors to consider are choice of processor, amount of memory, and selection of storage. This topic provides guidelines for storage configurations that provide good performance for Exchange Server. For detailed guidance and recommended processor configurations, see Planning Processor Configurations. For detailed guidance and recommended configurations for memory, see Planning Memory Configurations.

This topic provides guidelines for selecting a storage configuration that provides good performance and a strong platform for Exchange 2007. Capacity and performance are often at odds with each other when it comes to selecting a storage solution, and both must be considered before making a purchase. Generally, the decision involves the following factors:

Making sure there will be enough space to store all of the data. Determining your capacity needs is a relatively straightforward process.

Making sure the solution provides acceptable disk latency and a responsive user experience. This is determined by measuring or predicting transactional input/output (I/O) delivered by the solution.

Making sure that non-transactional I/O has both enough time to complete and enough disk throughput to meet your service level agreements (SLAs).

The goal is to find a balance of these factors so that you can design the actual hardware solution for your servers.

Disk subsystem bottlenecks cause more performance problems than server-side CPU or RAM deficiencies. A poorly designed disk subsystem can leave your organization vulnerable to hardware malfunctions. Specifically, your disk subsystem is considered to be performing poorly if it is experiencing:

Average read and write latencies greater than 20 milliseconds.

Latency spikes greater than 50 milliseconds that last for more than a few seconds.

High disk latency is synonymous with slow performance. To reduce costly disk latency issues, at a minimum, you should:

Invest in high performance disks and spindles It is better to have smaller capacity disks that utilize each spindle's performance than to use fewer spindles with large capacity. Fast storage with a sufficient amount of spindles is one of the most important investments you can make in your messaging infrastructure.

Consider performance before capacity Relying on capacity as the primary metric for storage sizing often results in poor performance for your disk subsystem. For example, most administrators who select a RAID-5 solution do so to maximize storage usage. However, in many cases, properly sizing the performance of your spindles requires you to use more physical disks for RAID-5 than you would use in a RAID-1+0 configuration.

Align your disks Use the Diskpart.exe tool to verify that your disk tracks are sector-aligned. By using Diskpart to create aligned partitions (as compared with non-aligned partitions that are created with the Disk Management snap-in or Windows Explorer), you can increase disk performance by as much as 20 percent. Note that Diskpart can only be used with basic disks. Diskpart cannot be used with dynamic disks. Diskpart is part of the Windows Server 2003 Service Pack 1 Support Tools. Diskpart supersedes the functionality found in Diskpar, a Windows 2000 Server Resource Kit tool.

In general, to optimize your storage system and avoid high disk latency issues, you need to understand:

The causes of Exchange 2007 disk I/O. Understanding all sources of disk I/O activity is necessary to design a storage solution that can handle the expected workload. For details about the various causes of Exchange 2007 disk I/O on the various server roles, see What Causes Exchange Disk I/O.

How to calculate your disk I/O, and disk capacity requirements. Undersized storage solutions can cause a poor user experience, and running out of disk space can cause unexpected and unwanted outages. It is important that your storage solution be designed with both performance and capacity in mind. For detailed guidance on how to calculate the disk I/O requirements for your Exchange 2007 servers and design an appropriate storage solution, see Mailbox Server Storage Design and Transport Server Storage Design.

How to design your partitions. We recommend that you optimize your partitions for Exchange 2007. For guidance on the recommended partition design for your Exchange 2007 servers, see Partition Design.

What storage technology you should use. For an overview of the supported storage technologies for Exchange 2007 and a comparison of RAID types, see Storage Technology.

How to verify the performance of your storage system. It is very important to validate your storage solution configured exactly how you plan to deploy it before going into production. For details on how to verify the performance of a storage solution, see Storage Validation.